Use tonal pairs for cached token bands

[edwin-zvs]

Summary

• render cached and fresh token usage as solid same-hue tones instead of mixed-density glyphs
• preserve both parts when their boundary shares a terminal cell, eliminating false three-section bars
• keep the original single-dot legend shape, with a darker dot and brighter same-hue model text
• keep tonal pairs distinct after ANSI 256/16 quantization
• update the fleet token-meter design spec to record the tonal-pair semantics

Testing

• env -u NO_COLOR TERM=xterm-256color COLORTERM=truecolor cargo test -p construct-cli (1311 unit tests + reconnect integration test passed)
• cargo test -p construct-cli legend (12 passed after legend follow-up)
• cargo test -p construct-cli cached (14 passed after legend follow-up)
• cargo build
• git diff --check
• deterministic before/after VHS recording, visually verified at midpoint

[edwin-zvs]

Visual comparison

Before

After

[edwin-zvs]

Visual comparison

Before

After

[edwin-zvs]

Updated after recording: single darker legend dots with brighter same-hue labels.